diff --git a/includes/add_datastream.form.inc b/includes/add_datastream.form.inc
index 3a1d964d..33decefc 100644
--- a/includes/add_datastream.form.inc
+++ b/includes/add_datastream.form.inc
@@ -161,7 +161,10 @@ function islandora_add_datastream_form_validate(array $form, array &$form_state)
   if (isset($form_state['datastream_requirements'][$dsid]) && $file) {
     $allowed_types = $form_state['datastream_requirements'][$dsid]['mime'];
     $mime_detect = new MimeDetect();
-    $allowed_extensions = array_map(array($mime_detect, 'getExtension'), $allowed_types);
+    $allowed_extensions = array();
+    foreach ($allowed_types as $mime) {
+      $allowed_extensions = array_merge($allowed_extensions, $mime_detect->getValidExtensions($mime));
+    }
     $errors = file_validate_extensions($file, implode(' ', $allowed_extensions));
     if (count($errors) > 0) {
       form_set_error('file', $errors[0]);
diff --git a/includes/mime_detect.inc b/includes/mime_detect.inc
index 4035afe5..c275f150 100644
--- a/includes/mime_detect.inc
+++ b/includes/mime_detect.inc
@@ -383,4 +383,19 @@ class MimeDetect {
     return $this->protectedMimeTypes;
   }
 
+  /**
+   * Get all valid extensions for this MIME type.
+   *
+   * @param string $mimetype
+   *   The MIME type we are searching for.
+   *
+   * @return array
+   *   An array of valid extensions for this MIME type.
+   */
+  public function getValidExtensions($mimetype) {
+    $filter = function($mime) use ($mimetype) {
+      return $mime == $mimetype;
+    };
+    return array_keys(array_filter($this->protectedMimeTypes, $filter));
+  }
 }